Flow control valves used in plumbing are available in a variety of forms. In recent years, the trend has been to use cartridge-like assemblies which include a valving element as well as an associated valve seat. With this type of construction, the entire cartridge is considered disposable and is replaced when one of the elements is worn. Some of these units include an inexpensive valve body constructed of a moldable material such as plastic. A stem is rotatable within the valve body member and includes a tapered seat which coacts with a seating surface formed on the valve body to control the flow of water through the valve cartridge. An interference type engagement between the tapered valve seat and the valve body provides the necessary control function. An example of such a valve can be found in U.S. Pat. No. 3,789,870.
To provide the necessary sealing, flexure in the valve body when contacted by the tapered valve seat is required. In addition, it is believed that in order to provide the necessary longevity, the stem must be constructed from both a corrosion resistant and hard material such as brass. As a result, the overall valve construction can be expensive.
An all plastic construction has also been suggested in the prior art. For example, in U.S. Pat. No. 3,967,811 spring loaded sealing elements carried by a rotatable stem rotate into and out of alignment with flow passages. When aligned with the flow passages, water is allowed to proceed from an inlet, through the sealing elements and into a passage feeding a faucet or spigot. The fluid seal between the valve elements and the valve body is provided by springs which urge the elements into tight, confronting engagement with a sealing surface formed in the valve body. Surface irregularities in either the valve body or the sealing elements are likely to cause leakage. Moreover, foreign matter passing through the valve body can easily damage the sealing surfaces, necessitating replacement of the entire cartridge.